SECS/GEM Data Items

Status Variables (SV)

Status variables are data items that identify the status of the equipment, or any of its components, such as sensors, meters, etc. Examples of status variables for process equipment are – Temperature, Pressure, Gas Flows, RF Forward Power, Spin Speed, etc. These data items are generally not attached to events such as lot start, wafer start, etc. A factory host can query the status variables to the equipment any time or can define trace data setup through which it asks the equipment of supplying status variables at regular intervals. A factory host cannot change status variables of the equipment.

Data Value Variables (DV)

Data value variables are data items that are related to a certain event, such as lot start, alarm/error occurring on the equipment, wafer processing/measurement complete, etc. Examples of data value variables are – LotID, SlotNumber, CurrentRecipe, etc. These variables change only when a certain event occurs, such as selecting a recipe, starting lot processing, etc. A factory host queries Data Value variables through defining reports and associating the reports to events.

Unlike status variables, data value variables may not have a value. For example, one of the data value variable is AlarmID, which designates the ID of the most recent alarm. However, it can be empty if there haven’t been any alarms since the equipment was turned ON. A factory host cannot change the data variables of the equipment.

Equipment Constants (EC)

Equipment constants are data items related to the configuration of the equipment – they could contain items related to the equipment hardware, software or SECS/GEM software. Unlike status variables and data value variables, a factory host can change equipment constants through SECS messages. Examples of equipment constants are – PumpDown Time Limit, Equipment Standby Time, Pins Up Wait, etc.

Data Properties:

The Data types listed above have similar properties so that it’s convenient to define the data. The equipment supplier is required to provide these properties in a SECS/GEM manual so that the fab host will be able to understand and communicate with the data. Below are some of the important data properties of the Data Types:

• ID – It’s a numeric ID that must be unique in the SECS/GEM interface. These IDs can be grouped by data type and are referred to as SVIDs (Status Variable IDs), DVIDs (Data Variable IDs) and ECIDs (Collection Event IDs).
• Name – It’s a name assigned to a data item so that we can identify it easily.
• Format –Data type of the item.
• Data formats can be simple (numeric, ASCII, Boolean) or complex (arrays, lists, structures). For example, numeric types can be I1, I2, I4, I8 (signed integer types of different byte length), U1, U2, U4, U8 (unsigned integer types) and F4 or F8 (floating point types).
• Array types and List contain multiple values in the data item. For example, image data will be formatted as a Byte Array.
• Structure types contain a specific type of data. For example, a variable may represent a slot map which contains carrier information and also list of slots with their wafer placement status.
• Value –It’s the actual value of the data item. Data values are in an accurate, efficient, self-describing binary format so that its easy for the host to interpret the data. The data format allows collection of more data and with more efficiency.

Alarms & Collection Events (CE) also have IDs and names for their identification.

Data Polling :

The fab host often gets data on a regular intervals through event reports & trace reports and that it defines. SECS/GEM also provides a system for the fab host to poll data based on its needs.

Fab Automation services.